1. Field of the Invention
This invention relates to a shielded flat ribbon cable and a method for fabricating a shielded flat ribbon cable.
2. Description of the Related Art
Shielded flat ribbon cables are used within electronic equipment as wiring.
For example, Japanese Utility Model Laid-Open No. 63-127018 (JP-U 63-127018) discloses a shielded flat ribbon cable having a plurality of insulated wires comprising conductors and insulations coating the conductors respectively, in which the insulated wires are covered pair by pair with an individual shield layer and an electrically conductive polymeric resin. The pair of the insulated wires, the individual shield layer and the electrically conductive polymeric resin constitute an inner sheathed wire, and a plurality of the inner sheathed wires are covered with bundling (collective) insulating layers and bundling (collective) shielding layers.
Also, for example, JP-U 63-127018 shows in FIG. 3 a shielded flat ribbon cable as a prior art, in which one pair of insulated wires and an inner sheath covering these insulated wires constitute an inner sheathed wire. A plurality of the inner sheathed wires are disposed in parallel to each other with a spacing, and are covered with bundling shielding layers and bundling (collective) outer jackets. The bundling shielding layers form bridging portions between the adjacent inner sheathed wires, and the facing bundling shielding layers are in pressure contact with each other in the bridging portions.
On the other hand, as a transmission medium suitable for high frequency signal transmission, semi-rigid cables are also known. The semi-rigid cable has a copper pipe as an outer conductor, and an inner conductor and an insulation thereof are covered with the copper pipe.
The copper pipe of the semi-rigid cable is constant in inner diameter, and smooth in inner surface, and seamless in circumferential direction. For these reasons, the use of the semi-rigid cable lessens variation in characteristic impedance, so that it is easy to match load impedance, thereby suppressing the transmission loss, even when its skin effect is significant due to high frequency signal transmission.